As a method of judging the truth of a bill, a method disclosed in Japanese Patent Publication No. 215293/1985 has been known. In this method, a bill is divided into a plurality of regions. Detection data is obtained by a magnetic sensor for each region of a bill to be examined. The ratio of the detection data in each of the regions to the sum of the detection data in all the regions is calculated for each region. The ratio calculated for each region is compared with a reference value previously found for the region. If the difference therebetween is not within a predetermined allowable range in any one of the regions, it is judged that the bill is a false bill.
If the difference therebetween is within a predetermined allowable range in all the regions, the sum of the differences between the ratios calculated for the respective regions and the reference values in the corresponding regions is calculated. If the calculated sum is not less than a predetermined allowable value, it is judged that the bill is a false bill. If the calculated sum is less than the predetermined allowable value, it is judged that the bill is a true bill.
In the above-mentioned prior art, the ratio of the detection data in each of the regions to the sum of the detection data in all the regions is compared with the reference value previously found for the region. In cases such as a case where the bill is uniformly dirty, therefore, the method of judging the truth of a bill in the prior art is not easily affected by the dirt. However, the dirt of the bill is not generally uniform in respective portions of the bill. In the above-mentioned prior art, erroneous judgment may be made by the dirt, the wrinkle and the like of the bill.
An object of the present invention is to provide a method of judging the truth of a paper type, wherein the truth of a paper type can be judged with high precision without being affected by the dirt, the wrinkle and the like of the paper type.
Another object of the present invention is to provide a method of judging the direction in which a paper type is fed, wherein the direction in which a paper type is fed can be judged with high precision.
Still another object of the present invention is to provide a method of calculating the width of shift of a waveform representing a characteristic amount of a paper type, wherein the width of shift in the direction of conveyance of a waveform representing a characteristic amount of a paper type from a reference waveform can be accurately calculated.